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Low-temperature wet chemical bath deposition (CBD) method is one of the most efficient and least hazardous solution-based techniques which is widely employed to grow ZnO NRs. In CBD method, a seed layer is usually deposited on the substrate. In this paper, high quality ZnO and aluminum doped ZnO (AZO) seed layers are sputtered on the indium tin oxide (ITO) coated glass. In continue, aligned ZnO NRs are grown on the AZO and ZnO seed layers via CBD technique. The effect of the growth time and seed layer on the physical properties of as-grown ZnO NRs are investigated. According to the results, the seed layer plays an essential role on the growth orientation and growth rate of the ZnO NRs. The ZnO NRs grown on AZO seed layer are more aligned rather than ZnO seed layer due to their higher texture coefficients. The relative photoluminescence (PL) intensity ratio of near band emission (NBE) to deep level emission (DLE) (I NBE /I DLE ) for the ZnO NRs grown on AZO and ZnO seed layers are calculated as 7.45 and 2.62, respectively. To investigate the performance of the as-grown ZnO NRs, near ultraviolet organic light-emitting diodes (UV-OLEDs) using ZnO NRs array as n-type material and poly [2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene-vinylene] (MEH-PPV) conjugated polymer as p-type material have been fabricated. The total concentration of traps ( N t ), the characteristic energies ( E t ) and the turn-on voltages for the devices with the structures of ITO/AZO/ZnO NRs/MEH-PPV/Al (device A) and ITO/ZnO/ZnO NRs/MEH-PPV/Al (device B) are attained 7.65 × 10 16 and 7.75 × 10 16 cm −3 , 0.232 and 0.206 eV, 23 and 21 V, respectively. Moreover, based on the electroluminescence (EL) spectra, the NBE peaks for device A and B are obtained nearly in the wavelengths of 382 and 388 nm, respectively. Finally, various charge carrier transportation processes of prepared UV-OLEDs have been studied, systematically. [ABSTRACT FROM AUTHOR]

• ZnO nanorods-based Metal-semiconductor-metal UV detector is designed and fabricated. • New simple nanorod growth precursor enhances response/recovery time and sensitivity. • Dark current and power consumption are reduced by adding alcohol to precursor. • Alcoholic growth precursor raises selectivity and illumination/dark current ratio. • Nanorods grown in alcoholic precursor are more monocrystalline, denser and thinner. In this paper, a strategy to simultaneously improve the response speed, selectivity and photosensitivity of ultraviolet photodetector is presented. Metal-semiconductor-metal ultraviolet photodetectors based on Zinc oxide nanorods are designed and fabricated. The ZnO nanorods of detectors have been synthesized by chemical bath deposition method in four different solvents of growth precursors (including pure deionized water and the solvent containing Methanol, Ethanol or Isopropanol and Deionized water). The optimal condition of synthesizing ZnO nanorods in the chemical bath deposition method is a temperature of 90 ℃ and 2.5 h of the growth process. The morphological, optical and electrical impact of OH source supplementary by adding alcohol on ZnO nanorod-based detector are investigated. The results indicate the supplement of alcohol to the precursor make the growth nanorods be more mono-crystalline and highly vertical. Nanorods growing in the Isopropanol are denser, longer and thinner. Moreover, the greater the concentration of OH ions in the growth precursor, the greater the selectivity of the photodetector is. Furthermore, the illumination-to-dark current ratio enhances from 2 orders of magnitude for pure deionized water solvent to 4 orders of magnitude for Isopropanol containing precursor. The results reveal the increase in the density of nanorods of the photodetector declines the dark current. In addition, the photosensitivity of the detector prepared in Isopropanol containing precursor is about 1.99 × 105 which is the highest sensitivity in comparison with the other detectors. The results of the transient response of photodetectors indicate the fastest response and recovery time are 12 s and 36 s, respectively, which belong to the Isopropanol containing precursor-based photodetector. Consequently, the ZnO nanorod-based photodetector with Isopropanol alcohol containing precursor makes precise detector due to its greater selectivity, greater photosensitivity, faster response and recovery time and lower power consumption. [ABSTRACT FROM AUTHOR]

The hydrogen gas sensing properties of carbon-doped ZnO nanotube has been theoretically investigated by employing first-principles density functional theory in combination with non-equilibrium Green's function. The figure of merits is creating the new states in ZnO nanotube structure by adding carbon substitution for an oxygen site. The calculation of adsorption energy indicates strong chemical adsorption of hydrogen on the outside and inside of carbon-doped ZnO nanotube. Moreover, density of state, current-voltage and sensor response have been performed for energetically favorable adsorption geometries of hydrogen. The involvement of carbon valence electrons in the chemical adsorption of hydrogen has been examined by partial density of state diagram. The current-voltage diagram of carbon-doped ZnO nanotube indicates negative-differential resistance trend. This trend has been disappeared after the chemical adsorption of hydrogen. The sensor response calculations reveal the high response of the sensor occurs in 3.5 V on the outside and inside of carbon-doped ZnO nanotube. • Investigation of energy adsorption and transfer properties of carbon-doped ZnO nanotube. • Strong chemical adsorption of hydrogen on the outside/inside of carbon-doped ZnO nanotube. • New states are observed in local density of state (LDOS) after the addition of carbon doping. • Examination of negative-differential resistance in I–V curves of carbon-doped ZnO nanotube. • High sensor response is occurred in voltage of 3.5 V. [ABSTRACT FROM AUTHOR]

Oxide semiconductor-based heterojunction bipolar transistors are widely applicable in flexible, printable, and cost-effective circuit applications. Among earth-abundant metal oxides, zinc oxide and copper oxide inherently show n-type and p-type characteristics, respectively, and their electronic properties can be easily modified during the fabrication process. Accordingly, a planar-type HBT can be achieved by low-temperature growth of the metal-oxide layers on a flexible substrate without the need for further sophisticated processes. In this paper, a double heterojunction bipolar transistor (DHBT) comprised of ZnO layers serving as the emitter and collector regions, along with the CuO layer functioning as the base area is presented. Simulation results demonstrate that the proposed all-metal oxide transistor based on p-CuO/n-ZnO heterojunction enjoys low power consumption owing to the low threshold voltage. High-frequency characterization and DC analysis of the proposed NPN configuration are carried out using the ATLAS/SILVACO package. Our findings reveal that at the base-emitter voltage of 0.55 V, the current gain factor of the device reaches 155, which is larger than those reported in the literature. Furthermore, an ideality factor at the base-emitter voltage of 0.7 V was obtained for the collector-base and emitter-base junctions equal to 1.5 and 1.2, respectively. • A CuO/ZnO-based double heterojunction bipolar transistor (DHBT) is designed and simulated. • The n-ZnO and p-CuO as emitter/collector and base layers suggest outstanding current gain and cutoff frequency. • DC and high-frequency characterizations of n-ZnO/p-CuO/n-ZnO DHBT are analyzed. • The unity-gain cutoff frequency is calculated 8.5 GHz accompanied by the AC gain of 9.53 dB. [ABSTRACT FROM AUTHOR]